CMS_decrypt(3) - NetBSD Manual Pages

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CMS_decrypt(3)                      OpenSSL                     CMS_decrypt(3)




NAME

       CMS_decrypt, CMS_decrypt_set1_pkey_and_peer, CMS_decrypt_set1_pkey,
       CMS_decrypt_set1_password - decrypt content from a CMS envelopedData
       structure


LIBRARY

       libcrypto, -lcrypto


SYNOPSIS

        #include <openssl/cms.h>

        int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert,
                        BIO *dcont, BIO *out, unsigned int flags);
        int CMS_decrypt_set1_pkey_and_peer(CMS_ContentInfo *cms,
                        EVP_PKEY *pk, X509 *cert, X509 *peer);
        int CMS_decrypt_set1_pkey(CMS_ContentInfo *cms, EVP_PKEY *pk, X509 *cert);
        int CMS_decrypt_set1_password(CMS_ContentInfo *cms,
                                      unsigned char *pass, ossl_ssize_t passlen);


DESCRIPTION

       CMS_decrypt() extracts the decrypted content from a CMS EnvelopedData
       or AuthEnvelopedData structure.  It uses CMS_decrypt_set1_pkey() to
       decrypt the content with the recipient private key pkey if pkey is not
       NULL.  In this case, it is recommended to provide the associated
       certificate in cert - see the NOTES below.  out is a BIO to write the
       content to and flags is an optional set of flags.  If pkey is NULL the
       function assumes that decryption was already done (e.g., using
       CMS_decrypt_set1_pkey() or CMS_decrypt_set1_password()) and just
       provides the content unless cert, dcont, and out are NULL as well.  The
       dcont parameter is used in the rare case where the encrypted content is
       detached. It will normally be set to NULL.

       CMS_decrypt_set1_pkey_and_peer() decrypts the CMS_ContentInfo structure
       cms using the private key pkey, the corresponding certificate cert,
       which is recommended to be supplied but may be NULL, and the (optional)
       originator certificate peer.  On success, it also records in cms the
       decryption key pkey, and this should be followed by "CMS_decrypt(cms,
       NULL, NULL, dcont, out, flags)".  This call deallocates any decryption
       key stored in cms.

       CMS_decrypt_set1_pkey() is the same as CMS_decrypt_set1_pkey_and_peer()
       with peer being NULL.

       CMS_decrypt_set1_password() decrypts the CMS_ContentInfo structure cms
       using the secret pass of length passlen.  On success, it also records
       in cms the decryption key used, and this should be followed by
       "CMS_decrypt(cms, NULL, NULL, dcont, out, flags)".  This call
       deallocates any decryption key stored in cms.


NOTES

       Although the recipients certificate is not needed to decrypt the data
       it is needed to locate the appropriate (of possible several) recipients
       in the CMS structure.

       If cert is set to NULL all possible recipients are tried. This case
       however is problematic. To thwart the MMA attack (Bleichenbacher's
       attack on PKCS #1 v1.5 RSA padding) all recipients are tried whether
       they succeed or not. If no recipient succeeds then a random symmetric
       key is used to decrypt the content: this will typically output garbage
       and may (but is not guaranteed to) ultimately return a padding error
       only. If CMS_decrypt() just returned an error when all recipient
       encrypted keys failed to decrypt an attacker could use this in a timing
       attack. If the special flag CMS_DEBUG_DECRYPT is set then the above
       behaviour is modified and an error is returned if no recipient
       encrypted key can be decrypted without generating a random content
       encryption key. Applications should use this flag with extreme caution
       especially in automated gateways as it can leave them open to attack.

       It is possible to determine the correct recipient key by other means
       (for example looking them up in a database) and setting them in the CMS
       structure in advance using the CMS utility functions such as
       CMS_set1_pkey(), or use CMS_decrypt_set1_password() if the recipient
       has a symmetric key.  In these cases both cert and pkey should be set
       to NULL.

       To process KEKRecipientInfo types CMS_set1_key() or
       CMS_RecipientInfo_set0_key() and CMS_RecipientInfo_decrypt() should be
       called before CMS_decrypt() and cert and pkey set to NULL.

       The following flags can be passed in the flags parameter.

       If the CMS_TEXT flag is set MIME headers for type "text/plain" are
       deleted from the content. If the content is not of type "text/plain"
       then an error is returned.


RETURN VALUES

       CMS_decrypt(), CMS_decrypt_set1_pkey_and_peer(),
       CMS_decrypt_set1_pkey(), and CMS_decrypt_set1_password() return either
       1 for success or 0 for failure.  The error can be obtained from
       ERR_get_error(3).


BUGS

       The set1_ part of these function names is misleading and should better
       read: with_.

       The lack of single pass processing and the need to hold all data in
       memory as mentioned in CMS_verify() also applies to CMS_decrypt().


SEE ALSO

       ERR_get_error(3), CMS_encrypt(3)


HISTORY

       CMS_decrypt_set1_pkey_and_peer() and CMS_decrypt_set1_password() were
       added in OpenSSL 3.0.


COPYRIGHT

       Copyright 2008-2023 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.



3.0.12                            2023-05-31                    CMS_decrypt(3)